A controversial procedure to limit the growth of severely disabled children to keep them forever small – which ignited a fiery debate about the limits of medical intervention when it was first revealed five years ago – has begun to spread among families in America, Europe and beyond.

The Guardian has learned that at least 12 other families have carried out or are in the process of undergoing such medical therapies. The total number of children who have been administered with hormones to keep them small may have reached more than 100 and interest among families extended into the thousands.

The Guardian is in contact with two of the new families, both involving severely disabled children who were adopted. They include the world's first known example of a boy who has been given hormone therapy that keep him child-sized for the rest of his life.

Five years ago details first emerged of Ashley, a nine-year-old girl living near Seattle. She was born with developmental disabilities that meant she was unable to talk or walk, and continues to have the cognitive ability of an infant.

Ashley's parents, together with doctors at Seattle children's hospital, devised a cocktail of medical interventions to keep her from growing any further. Dubbed the "Ashley treatment", the procedure was born out of the conviction that Ashley's quality of life would improve as it would spare her physical discomfort and pain.

The core of the treatment was hormone therapy: high estrogen doses to bring forward the closure of the growth plates in her bones, which would in turn stop her growing. In addition, surgical interventions included removal of her nascent breast buds to avoid the discomfort of fully-formed breasts later in life, and a hysterectomy to avoid menstruation.

In an email exchange with the Guardian published today, Ashley's father, who has kept a blog on his daughter's condition, says that five years later he remains convinced that the intervention has improved his daughter's life. Going under the name AD (Ashley's dad) to preserve his family's anonymity, he says "the Ashley treatment has made her far more likely to be comfortable, healthy and happy. Given the limitations imposed by her medical condition, her life is as good as we can possibly make it."

He also reveals that after Ashley's medical treatment was made public – sparking a global media firestorm and prompting outrage from several disability groups – many other families with severely disabled children contacted him for advice on how to follow his example. AD says that a private discussion group, called "pillow angels quality of life support group", was set up between him and six other families who have all by now completed the course of hormone doses – and in some cases surgery – that in effect freeze-frames their children at a small size.

There are "at least as many who are in progress" with the treatment, AD says, adding that in his calculation ten times as many have gone ahead under their own initiative.

Details of the six families who have conducted the medical interventions are sketchy, given the anonymity upon which they insist. It is known that four of the families live in the US, one in Europe and one in Oceania. Two of the six children are boys.

Curt Decker, director of the National Disability Rights Network, says he believed that thousands of families were actively exploring the possibility of practising the Ashley treatment. His group, which provides legal services to disabled people across the US, is preparing a report to be published in April that will call on Congress, states and individual hospitals to introduce new laws to ban growth attenuation treatment for disabled children.

"This is a violation of the civil rights of individuals, and it should be prohibited," Decker said. "Parents have rationalised that this is an OK thing to do, but it treats people as though they have no worth and that's a slippery slope that could end with the idea that people with disabilities don't have to be kept alive or integrated in society."

Silvia Yee, a lawyer with the Disability Rights Education & Defense Fund that is run jointly by disabled people themselves and parents of children with disabilities, said: "This is what we were fearing. It is becoming just one more choice on the menu of possibilities – a medical operation that will change a person's life. Who has the right to decide to change an individual into a different entity?"

The mothers of two of the children who have followed Ashley's example insist that they made the decision out of their child's best interests. Tom, who is now 12, is the first known boy to be given the intervention. He was seven when he had the procedure.

Tom's parents adopted him from Vietnam when he was a baby. They live in a European country, the identity of which the Guardian knows but has agreed not to disclose.

Tom, which is not his real name, has severe cerebral palsy and epilepsy and cannot sit, talk, walk or eat. His mother said she wanted growth attenuation therapy for him because he was becoming too big for her and her husband to give him the care he needs.

She rejects the argument that the therapy was a form of disrespect for her child: "It's the opposite. It will help Tom a lot and I will be grateful for the rest of my life for what [Ashley's family] did."

Tom's mother said that she was unsure whether the hormone therapy he underwent to keep him small was granted any official approval. "Our doctor told me that there is still no official protocol; cases are assessed one by one."

The other family in contact with the Guardian is that of Erica (also not her real name) who lives in the upper midwest of the US. Erica, 14, is also adopted, and was given a hysterectomy and hormone therapy based on the model of the "Ashley treatment" by doctors at the University of Minnesota. She began the treatment when she was 10.

Erica's mother said: "People don't understand we are talking about a small percentage – just one percent of the disabled population with disabilities like Erica's – who would be candidates for this treatment … People think you are playing God or messing with nature. But our loving God wouldn't want Erica to be in pain. She has a right to a happy life."

Both Tom and Erica's stories will be told by the Guardian in full on Friday.

In his email exchange with the Guardian, Ashley's father counters the criticism levelled at him by disability rights campaigners. In his opinion, "the treatment makes Ashley more dignified by providing her with a better quality of life. Depriving her of the treatment's benefits would be taking away from her human rights."

But he says that the controversy aroused around the Ashley treatment has discouraged many hospitals and doctors from becoming involved. Some parents with whom he is in touch have had to cross US state or even international borders to find willing medical participants.

In Washington state, where his family lives, the Washington Protection & Advocacy System investigated the therapy and concluded in a 38-page report published in May 2007 that Ashley's rights had been violated by the hormone doses and removal of her uterus and breast buds. To have gone ahead without a prior court order was a violation of the US constitution and Washington law, it found.

On the back of the report, the hospital that had carried out the procedures promised never to do so again without court permission.

Ashley's father says that he had been given legal advice to the contrary, and adds that the erection of judicial barriers only succeeded in harming the children. "The impact is that many families are not able to provide the treatment, so severely disabled children are deprived and the treatment becomes exclusive to the wealthy and powerful," he says.

With the revelation that many other families have now followed AD's example and gone ahead with the controversial therapy, the ethical and legal debate that surrounds it can only intensify.